The present invention relates to a plasma generating method and apparatus utilized in a process for manufacturing a semiconductor or a thin film circuit.
Recently, fine processes using a plasma have become popular in processes for manufacturing semiconductors or thin film circuits. More particularly, in dry etching, CVD, a doping processes, and gas suitable for a desired purpose is introduced into a vacuum chamber which has electrodes, and a high frequency electric power is applied to the electrodes to relatively simply carry out those processes. Thus, such fine processes using plasma are used in many processes.
For example, in the dry etching process, it is indispensable to make patterns fine, prevent ion scattering, and improve the directional properties of ions. Therefore, it is effective to increase the degree of vacuum and then to increase the mean free paths of the ions. Then, etching is effected under a high degree of vacuum.
Generally, as the degree of vacuum increases, the generation of a high frequency becomes more difficult. To prevent such a disadvantage, a method in which a magnetic field is applied to a plasma chamber to make the discharge easy, that is, a magnetron discharge or ECR (electron cyclotron resonance) discharge has been developed.
FIG. 3 is a schematic diagram showing a conventional dry etching apparatus using a magnetron discharge. In a vacuum chamber 29, a reactive gas is introduced through a gas controller 30 to control the pressure to become suitable by an exhaust system 31. An anode 32 is provided on the upper portion of the chamber 29 and a sample table 33 as a cathode is provided on the lower portion thereof. The table 33 is connected to an RF source 35 through an impedance matching circuit 34 to generate a high frequency discharge between the holder 33 and the anode 32. In the chamber 29, a magnetic field is applied thereto by an alternative electromagnet 36 provided on the side surface thereof to make the discharge easy in a high degree of vacuum. The applied magnetic field allows the cycloid movement of electrons to increase the ionization rate.
However, it is difficult to treat the magnetron discharge or ECR discharge because of uneven plasma density. A sample to be processed is subjected to any damage in such a discharge. For example, in a conventional magnetron dry etching apparatus, there is local plasma bias in accordance with the magnetic field to produce the local potential. Then, when the apparatus is used for manufacturing MOS LSIs, the destruction of gate oxide films is caused. Similarly, in the conventional ECR etching apparatus, the magnetic field has distribution in a radial direction of the chamber to cause uneven etching and to produce a local potential, on the basis of locally uneven plasma degrees.